This invention relates to a method for preventing fuel from infiltrating a microporous polymer membrane and a fuel deoxygenator device that uses the microporous polymer membrane to remove dissolved oxygen from fuel.
In a fuel system such as for an aircraft, fuel is mainly used to generate power. However, it also may be utilized as a coolant for various systems of the aircraft. Effective use of jet fuel as a coolant allows increases in operating temperatures of the aircraft and more efficient operation of the aircraft systems.
Jet fuel, like many other liquids, may absorb quantities of atmospheric gases. When jet fuel is in contact with air, oxygen from the air dissolves into the fuel. The absorbed gases may alter the chemistry of the fuel and affect the performance of the aircraft. For instance, the dissolved oxygen may react when heated above about 150° C. to form a free radical species. The free radical species initiate autoxidation reactions in the jet fuel that lead to the formation of carbonaceous deposits called “coke”.
The presence of dissolved oxygen and coke deposits has several detrimental effects. First, the coke deposits may be carried through the fuel delivery system of the aircraft and hinder the functionality of various components in the system. Second, the presence of oxygen and formation of coke deposits limit the use of the jet fuel as a coolant. For instance, jet fuel with dissolved oxygen forms coke deposits above about 150° C., so the operating temperature of the aircraft system cooled by the jet fuel is limited to about 150° C. to minimize the formation of the coke deposits. On the other hand, if the jet fuel is deoxygenated, it may be heated to about 450° C. without forming significant coke deposits.
There is at least one existing method of gas separation that may be suitable for removing dissolved oxygen from the jet fuel; however, the existing membranes for use with this method are not suitable. The method involves transferring a gas between two fluids through a membrane filter. This known method has been used for separating a particular gas from a mixture of gases or separating a particular gas dissolved in an aqueous solution but has not been entirely successful for jet fuel because of insufficient quality of the membranes.
One device for removing dissolved oxygen uses a gas-permeable membrane disposed within the fuel system. As fuel passes along the permeable membrane, oxygen molecules in the fuel diffuse out of the fuel across the gas-permeable membrane. An oxygen partial pressure differential across the permeable membrane drives oxygen from the fuel as it passes over the membrane.
Conventional gas-permeable membranes used in the above devices are produced using known methods such as solvent casting, melt casting, or other coating technique. The conventional membranes produced using these techniques have not yielded a membrane of sufficiently high quality for separation of oxygen in jet fuels though.
One of the primary detriments of conventional membranes is the effect of “micropores” in the membrane. Micropores are the free volume space between the molecules of the polymer that makes up the membrane. The free volume space forms a pathway, or micropore, through the membrane that enables molecules to permeate, i.e., migrate, from one side of the membrane to the other side of the membrane. In conventional membranes the size of the micropores is too large, allowing fuel, for example, to migrate into and infiltrate the membrane. As fuel infiltrates the membrane, the membrane becomes less effective in removing dissolved oxygen and incapable of sufficiently removing dissolved oxygen from the fuel.
Accordingly, a method for preventing fuel infiltration into a microporous polymer membrane is needed for such oxygen removing devices.